In order to improve the spectral efficiency of radio products, transmitter modulating schemes which produce a variable RF envelope are becoming increasingly common. In order to minimize off-channel splatter with these modulation schemes and still maintain acceptable RF power amplifier (PA) efficiencies, a number of PA linearization schemes have been developed.
FIG. 1 is a typical input-output characteristic of a power amplifier, as in the prior art. There is shown an X-Y plot, with the abscissa (X-axis) representing the input voltage and the ordinate (Y-axis) representing the output voltage. The curve 101 represents the relationship of the V.sub.output (Y-axis) to the V.sub.input (X-axis) for a typical amplifier. The curve 101 includes three portions, a first linear portion 105, a clipping portion 109, and a non-linear transitional portion 107. Those skilled in the art will appreciate that the output distortion corresponding to an operating point in the linear portion 105 is low, and increases as the operating point moves from the linear portion 105 to the transition portion 107. In order to maximize the efficiency of the amplifier, therefore, it is desirable to operate at the point on the curve 101 corresponding to largest possible value of V.sub.out, while still achieving an acceptable value of output distortion. For a low value of distortion, this operating point is represented as point 113 on curve 101. As shown, point 113 corresponds to an input of V.sub.A and an output of V.sub.B, and is situated at the junction of the linear portion 105 and the non-linear transitional portion 107. If more distortion were allowable, of course, then operating point 113 could be moved into the transitional portion 107, thereby providing a larger V.sub.B. The problem addressed by the invention, then, is--for a given level of distortion--how to set amplifier input level V.sub.A resulting in the highest possible output V.sub.B so that power output and efficiency are maximized.